1. Field of the Invention
The present invention relates to an improved closure liner and, more specifically, to a multi-layer closure liner having an improved gas barrier characteristic and particularly suited for use with container closures for carbonated beverages or the like.
2. Brief description of the Related Art
Plastic containers have become widely used and commercially successful for holding and storing a wide variety of products. For example, plastic containers are now widely used to contain carbonated beverages. In fact, most bottles containing carbonated beverages are produced from polyethylene terephthalate (PET) or a similar material, which provides a low cost, light weight and durable container. Such containers are typically provided with a polyolefinic resin cap or closure and an ethylene vinyl acetate (EVA) liner.
One problem with the use of such containers for carbonated beverages is that this type of closure and liner have a relatively high gas transmission rate. Carbonated beverages rely on the maintenance of a certain amount of carbon dioxide gas pressure in the container to maintain the carbonated quality of the beverage. The problem, however, is that this type of container for carbonated beverages has a limited shelf life due to the gas transmission rate of the PET bottle, the polyolefinic closure and the EVA liner. In other words, such containers, closures and liners permit loss of carbonation because the resins used provide only a limited barrier to escaping carbon dioxide gas. Another and somewhat lesser problem, is that the container, closure and liner allow oxygen to enter the container which can degrade the taste of carbonated beverages over time and/or adversely affect other characteristics of a product contained therein.
The prior art has attempted to reduce the gas transmission rate of the container itself by providing a layer of resin therein having little or no permeability to gases, as evidenced, by U.S. Pat. Nos. 5,472,573; 4,391,863, 5,238,718; 4,980,211; 4,564,541; 4,451,512 and 4,528,219. While these prior art techniques have been helpful in reducing gas loss though the container itself, a significant amount of gas is still lost through the closure, including the closure liner.
Thus, a need exists for an improved closure liner having suitable compressibility and other physico-mechanical properties of existing EVA liners, but which prevents or significantly reduces gas transmission through the closure of the container, thereby extending the shelf life of carbonated beverages and the like.